The present invention pertains to antennas. In particular, the invention relates to compact antennas with increased bandwidth.
Antennas are an important component of all wireless communication systems and are particularly important for mobile wireless communication terminals (e.g., wireless telephones, personal communication devices, personal digital assistants (PDA), portable global position system (GPS) devices, web pads, laptop personal computers (PC), tablet PC, etc.). Over time, these mobile wireless communication devices have become smaller in size and lighter in weight. This is particularly true for wireless telephones.
Further, more and more functionality is being incorporated into wireless telephones and personal communication devices. In fact, various devices are starting to be combined into a single all-in-one personal computing and communication device that may need wireless communications with broader frequency bandwidth, for example, having multiple frequencies. Such devices could be supported by multiple antennas incorporated in the single multi-function device. However, multiple antennas generally would require multiple transceivers or a more complex transceiver with some type of power driver network for splitting the drive signal among the plurality of antennas and a method of switching between the plurality of antennas. This would add size and weight to the mobile device.
The increased device functionality and reduction in device size and weight of wireless mobile communication devices continues to push the emergence of antenna designs that are more compact and lightweight, and have broader bandwidth communication capability. Now and in the future, more compact lightweight antenna designs with broader bandwidth are needed for mobile wireless devices, particularly antennas that operate in the 300 MHz-3000 MHz frequency range. However, a single antenna having smaller size and broader bandwidth may be difficult to achieve because bandwidth is generally proportional to the volume of an antenna. Therefore, a compact or miniaturized antenna that would be small in area and lightweight will typically result in narrow bandwidth.
A number of compact and multi-frequency-band antennas have been proposed. For example, micro-strip or patch antennas, such as the planar inverted-F antenna (PIFA) has been used for mobile telephones. (See, for example, K. Quassin, xe2x80x9cInverted-F antenna for portable handsetsxe2x80x9d, IEEE Colloqium on Microwave Filters and Antennas for Personal Communication Systems, pp. 3/1-3/6, February 1994, London, UK.) As suggested by its name, a patch antenna includes a patch or conductive plate. The length of the patch is set relative to the wavelength xcex0 of a desired transmission and/or reception frequency. A quarter wave patch antenna will have the length of the patch set at xc2xc xcex0. FIGS. 1A and 1B provide an exemplary prior art PIFA 100. Referring to FIG. 1A, the PIFA includes a ground plane 105, a planar patch 110, a grounding pin 120, and a feeding pin 115. A signal source and/or receiver 125 is connected to the feeding pin 115 for radio wave reception and/or transmission to and/or from the PIFA. The feeding pin 115 is connected to the planar patch 110 and signal source and/or receiver 125. The planar patch 110 is connected to the ground plane 105 by ground pin 120. FIG. 1B is a cross section view of the PIFA taken across line IB of FIG. 1A. The planar patch 110 of PIFA 100 provides the resonating antenna surface for wireless communications over the air waves. Although small in size, the PIFA has a relatively narrow bandwidth. The bandwidth is limited mainly by the height of the patch 110 relative to the ground plane 105.
Micro-strip antennas are low profile, small in size and light in weight. However, as mobile wireless communication devices become smaller and smaller, both conventional microstrip patch and PIFA antennas may be too large to fit the small mobile device chassis or the space available for an antenna(s) in a multi-function wireless device. This is particularly problematic when new generation mobile wireless communication devices need multiple frequencies (and possibly multiple antennas) for cellular, wireless local area network, GPS and diversity (e.g., Global System for Mobile communications (GSM) and Personal Communication System (PCS)).
Recently, Lai, Kin, Yue, Albert et al. proposed in Patent Cooperation Treaty (PCT) publication No. WO 96/27219 a meandering inverted-F antenna. With this antenna the size can be reduced to about 40% of conventional PIFA antenna.
Some devices, such as the all-in-one device (e.g., an integrated PDA and telephone) or a mobile telephone with diversity may be served by a multi-band antenna. Typically in the past, multi-band antennas have been directed to supporting two operating frequencies. One such antenna is the dual-frequency band PIFA proposed by David Ngheim in PCT publication WO 98/44588. This antenna has two separate adjacent patches that resonate at different frequencies that are interconnected by a common electrical single feed connection. Another such antenna was proposed by Davie Ngheim in U.S. Pat. No. 6,008,762. This antenna uses a folded quarter wave patch antenna to achieve dual frequency band operation. A still further dual-frequency antenna has been proposed by Rowell and Murch in the paper titled xe2x80x9cA Compact PIFA Suitable for Dual-Frequency 900/1800-MHz Operation,xe2x80x9d IEEE Transactions on Antennas and Propagation, Vol. 46, No. 4, April 1998. This antenna includes a capacitive feed and a capacitive load.
Unfortunately, none of the previously proposed antennas provide a satisfactory solution for the small size, light weight, broad bandwidth coverage needed by the upcoming new generations of wireless mobile communication devices operating in the 300 MHz-3000 MHz frequency range with minimal antenna return power loss. In particular, one recently developed application calls for a multi-function four band (quad-band) mobile terminal covering GSM800 (824-894 MHz), GSM900 (880-960 MHz), GSM1800 (1710-1880 MHz) and GSM1900 (1850-1990 MHz). None of the above mentioned antennas can meet this requirement. The presently known antennas do not have enough bandwidth to be used directly in this four band application without incurring significant loading loss at one or more of the desired operating frequency bands.
It should be emphasized that the term xe2x80x9ccomprises/comprisingxe2x80x9d when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence of addition of one or more other features, integers, steps, components or groups thereof.
Generally, the present invention includes compact antennas utilizing capacitive coupling between multiple conductive plates that achieves broad bandwidth. The capacitive coupling between the conductive plates may create a variable capacitance, inductance, and/or impedance as a function of frequency that increases the bandwidth. The number and design of conductive plates may be set to achieve the desired bandwidth and/or the number of distinct transmission frequencies for a particular application. The antenna may include capacitive coupling for the antenna feed and capacitive coupling of a parasitic conductive plate.
To achieve compact size and broad bandwidth, the antenna may include, for example, three or more layers of conductive plates or traces. One layer may be a feeding patch, one layer may be a main patch, and one layer may be a secondary patch. The secondary patch may be a parasitic patch. The main patch and/or the secondary patch may include one or more distinct areas which will be resonant at predetermined desired frequencies that has wider bandwidth due to the capacitive coupling between the various conductive plates. All of the conductive plates may be micro-strips and approximately parallel to one another and may have connection pins approximately parallel with one another. The conductive plates may be approximately parallel with a substrate and the connection pins may be approximately perpendicular to the substrate and conductive plates so as to form an L shape with the conductive plates. The orientation of the various conductive plates may be in any order and two of the conductive plates may be adjacent to each other on the same plane. However, their respective connection terminals for connecting to ground or feed should be located relatively close to one another. The distance between the various conductive plates to one another and to the substrate may be set to tune the antenna to resonate at the desired frequencies. The substrate may include a dielectric and/or a ground plane. The conductive plates may be formed on an antenna carrier positioned above the dielectric and/or ground plane having air in between. The conductive plates may be of any geometrical shapes and be two dimensional (e.g., planar) or three dimensional.
In various embodiments, an antenna may be designed to operate approximately within four radio frequency ranges, for example, 824-894 MHz (GSM-800), 880-960 MHz (GSM-900), 1710-1880 MHz (GSM-1800), and 1850-1990 MHz (GSM-1900). The antenna may be referred to as a four band or quad-band antenna. The antenna in this case may have multiple conductive plates that resonate at multiple frequencies approximately within the desired frequency ranges. For example, the antenna may include three L shaped portions (or legs) each including a micro-strip conductive plate and connection pin, with configurations approximately parallel to one another. The L shaped portions may be in close proximity with one another and separated by, for example, a dielectric, to take advantage of capacitive and inductive coupling. Two of the L shaped portions may be adjacent to one another on the same plane or all three may be on three separate planes mounted on an antenna carrier above the ground plane. In one variation, the lower L shaped portion may be, for example, a feed patch with a feed pin that provides a connection to a transmitter, receiver, or transceiver. The upper L shaped portion may be, for example, a dual band main patch and ground pin that is designed of two different branches with different lengths and areas so as to handle two or three of the four desired resonant frequencies. The two branches may share a common junction and may be right angled rectangular traces that turn back in a spiral or U-type shape starting at a right angle from the common feed junction. The third L shaped portion may be, for example, a parasitic high band patch and ground pin designed to handle one of the two higher desired resonant frequencies. This L shaped portion may be located adjacent to and on the same plane as the upper L shaped portion, in between the upper L shaped portion and the lower L shaped portion, on the same plane as the lower L shaped portion, of below the lower L shaped portion. The three L shaped portions (or legs) may be separate from each other and a mounting substrate by dielectric material such as air, plastic, etc. The substrate may be, for example, a printed circuit board (PCB) including a ground plane and the L shaped portions or legs may be, for example, printed conductive traces formed on an antenna carrier or on a dielectric supported by the PCB. In one preferred variation, the dual band main patch is above the feeding patch and the parasitic high band patch is adjacent the dual band main patch. In another variation, the positions of the dual band main branch and the feeding patch may be inverted so that the dual band main branch is below the feeding patch and the parasitic high band patch is adjacent the feeding patch. All three patches are capacitively coupled to one another and designed to provide four resonant frequencies useful for radio communications while having only a single feed pin or terminal connection to a receiver, transmitter, and/or transceiver.
In another embodiment, the patches, and particularly the two branches of the dual band main patch, may have a T or double U shape. Alternatively, the dual band main patch may be segregated into two patches, a longer patch for lower bandwidth, and a shorter patch for the higher bandwidth. Various geometrical configurations are possible for the various antenna patches, including 3-dimensional plates.